Andrew Gibiansky created all these package stack.yamls with this commit:

> commit f9846b6b
> Author: Andrew Gibiansky <andrew.gibiansky@gmail.com>
> Date:   Tue Jun 7 17:26:47 2016 -0700
>
>     Separate stack.yaml for each package for simplicity

The resolvers for all these stack yamls originally agreed with the
root stack.yaml, but now they're way off, apparently out of neglect.
Let's just delete them.